With the increasing popularity of portable electronic devices, demand for portable energy sources is increasing, both for portable and non-portable devices. There is also a prevalent sentiment and desire to use energy sources that are environmentally friendly. A majority of batteries currently in such use are of the type that is generally referred to as lithium ion batteries (Li-ion or LIB). Li-ion batteries include cells that are rechargeable and use lithium ion migration from a cathode to an anode during discharge, and in the reverse direction when charging. Li-ion batteries commonly use an intercalated lithium compound as a cathode material, and have a relatively high energy density, a low degradation of performance over charge/discharge cycles, and a relatively slow discharge rate when not in use. Beyond small, portable electronic applications, Li-ion batteries are gaining popularity in larger applications such as electric vehicle and aerospace applications.
Aside from their high power density and repeatable performance characteristics, Li-ion batteries can be dangerous under some conditions. For example, Li-ion batteries may use a flammable electrolyte and should be kept pressurized and partially charged when transported. Moreover, lithium reserves are becoming scarce on a global scale, which increases prices and decreases availability of lithium for battery manufacturers and consumers.
One potential replacement for Li-ion batteries are batteries using sodium ion cells. The so called sodium-ion (Na-ion) batteries stand out because sodium is cheaper, non-toxic, and more abundant than lithium. Currently, one known drawback of Na-ion batteries is their long charge and discharge times. In general, there is a tradeoff between the charge/discharge rate and capacity, so that attempts to increase the charge/discharge rate have resulted in severely reduced capacity. Moreover, at present, widespread Na-ion cell or battery use has been generally unsuccessful because of the irreversible capacity loss attributed to formation of a solid electrolyte interface (SEI) layer on the surface of the cells' anodes, which blocks access of ions to the cell's electrodes, thus greatly shortening the energy producing life and capability of the cell.